Underground wires and the like, including for example electrical wires, communication and T.V. cables, etc., extend underground through conduits. These conduits, which may be made of many different materials such as steel, pre-cast concrete, PVC, fiber or clay tile are generally buried in layers of as few as two or as many as twenty or more which are stacked either directly on top of one another or arranged side-by-side or separated by thin layers of sand. Taken together, the plurality of conduits form a conduit bank which generally runs between underground cable vaults, a cable vault being the accessible underground space beneath a mancover or the like.
Individual conduits of a bank from time to time become inoperable. For example, an existing conduit may simply deteriorate or it may become obstructed due to damage or the settlement of various sections of the conduit bank. Or, an existing conduit may become obsolete as it would lack sufficient capacity to accommodate a modified new cable installation.
Until now, replacing a conduit necessitated excavation of the ground for the complete distance from one cable vault to the next, even if it were necessary to replace only one individual conduit of the conduit bank from end to end. Such excavation is both costly and time consuming. Further, if it is necessary to excavate for the entire length of the conduit bank, there is no means of replacing an individual conduit which is located within the interior of a conduit bank except by removing and replacing all of the surrounding conduits. This of course substantially increases the cost of replacement.
Replacement of an existing pipe, for example a water supply pipe, a sewage pipe or the like without excavation is known. In accordance with this technique, pits are dug down to the pipe at spaced apart locations. One enters the first pit, enters the pipe and inserts a device which moves through the pipe, effecting replacement thereof with a new pipe which is pulled therethrough until the device reaches the other pit, at which point it is pulled out or the process is continued. Such methods and apparatus are shown for example in the Streatfield et al U.S. Pat. No. 4,720,211, the Yarnell U.S. Pat. No. 4,789,268 and the Lindsay U.S. Pat. No. 3,181,302. However, notwithstanding the use of this trenchless technique (that is, in the sense that it does not require a continuous trench for the full length of the pipe being replaced) it remains the state of the art in the field of conduit banks for wires, cables and the like to excavate a trench for the entire length of the conduit bank.
Thus, there exists a need for an improved method and apparatus for replacing some or all of the individual conduits within a conduit bank of the type carrying electrical wires, cables and the like, which does not require full length excavation.
An alternative repair/replacement practice is to simply run a new conduit into an existing conduit. However, by necessity, the newer conduit would then have a smaller internal diameter than the existing conduit and thus will be of reduced wire or cable carrying capacity.